Openflow controller abstract connector

	- Add openflow_conn abstract impletation for all openflow connectors
	- Refactor all existing conenctor to Inherit la clase abstracta
	- Now all of connector raise an exeption in case of faliure
	- As OF_connector raise an expection, all code that make use of this class now capture the execption.
	- Add to ofc DB table last_error and status column
 	- Check for each operation if an error exist an update DB ofc status and last error column info

Change-Id: Ia3d3bf63fee79dd18d61aeeb08a983dfcb88b729
Signed-off-by: mirabal <leonardo.mirabal@altran.com>